1. Field of the Invention
The present invention relates to a drawing apparatus for fixing a sheet-shaped recording material to an outer peripheral surface of a drum to draw an image on the recording material.
2. Description of the Background Art
Drawing apparatuses have been used for drawing images upon irradiation of various types of photosensitive materials with light. In a drum-type drawing apparatus, a photosensitive material is mounted on a recording drum which is rotatable in a primary scanning direction, and a recording head comprising a laser diode and the like moves in a secondary scanning direction parallel to a rotary shaft of the recording drum to draw an image on the photosensitive material.
FIG. 34 is a schematic perspective view of a recording drum in a conventional drawing apparatus. A plate 160 made of aluminum serving as a photosensitive material is mounted on a recording drum 150 shown in FIG. 34. A front end clamp 170 for fixing one end of the plate 160 and a rear end clamp 180 for fixing the other end of the plate 160 are attached to an outer peripheral surface of the recording drum 150. The rear end clamp 180 contains a magnet, and is fixed by a magnetic force to a position, on the outer peripheral surface of the recording drum 150, corresponding to the size of the plate 160.
The recording drum 150 having the plate 160 attached thereto is rotated at relatively low speed around a rotary shaft 190, so that an image is drawn on the surface of the plate 160.
In recent years, a request to improve the efficiency of processing for drawing an image on the plate 160 has been made. In order to improve the efficiency of the drawing processing, the recording drum 150 having the plate 160 attached thereto must be rotated at high speed.
However, the rear end clamp 180 is fixed to the recording drum 150 by the magnetic force. When the recording drum 150 is rotated at high speed, therefore, the rear end clamp 180 moves on the outer peripheral surface of the recording drum 150 or is detached from the recording drum 150, so that the plate 160 fixed to the recording drum 150 may be shifted in position and detached. Therefore, the recording drum 150 cannot be rotated at high speed.